Brian, here's a solution, too, involving less woodworking.
1. Attach eyescrews (or eyebolts) along the edge of an eight-foot length of 1x2 poplar at whatever interval you want. Repeat for another length. Screw both assemblies to wall studs near the ceiling and near the floor. Now you've made an eight-foot square easel.
2. Securely tie paracord (designed to be "not stretchy," and it supports 550 pounds--Google "550 paracord" if you can't find a local source) to the upper right eyescrew, run it through whatever hanging devices you have attached to your canvas (more eyescrews?), up through the upper left eyescrew, and tie it off on the bottom left. Height of the canvas is controlled by tightening or loosening this cord.
3. Attach two bungee cords to the lower corners of the canvas and out laterally to the bottom eyescrews. These act as tensioners.
The disadvantage to this system is the need for multiple screw holes on the back of the canvas frame.